Surface wettability effects on flow in rough wall nanochannels

Abstract

The effect of rough-wall/fluid interaction on flow in nanochannels is investigated by NEMD. Hydrophobic and hydrophilic surfaces are studied for walls with nearly atomic-size rectangular protrusions and cavities. Our NEMD simulations reveal that the number of liquid atoms temporarily trapped in the cavities is affected by the strength of the potential energy inside the cavities. Regions of low potential energy are possible trapping locations. Fluid atom localization is also affected by the hydrophilicity/hydrophobicity of the surface. Potential energy is greater between two successive hydrophilic protrusions, compared to hydrophobic ones. Moreover, groove size and wall wettability are factors that control effective slip length. Surface roughness and wall wettability have to be taken into account in the design of nanofluidic devices. Keywords NEMD simulation Á Rough-wall nanochannels Á Surface wettability Á Fluid atom trapping Á Potential energy Á Effective slip length List of symbols F ext Magnitude of external driving force h Gap between channel walls K Spring constant k B Boltzman constant L x Length of the computational domain in the x-direction L y Length of the computational domain in the y-direction L z Length of the computational domain in the z-direction L s Slip length L s,eff Effective slip length m Atom mass N Number of atoms p Periodic roughness factor r eqPosition of a wall atom on fcc lattice site r i Position vector of atom i r ij Distance vector between ith and jth atom T Temperature u(r ij ) LJ potential of atom i with atom j V Volume of the computational domain (L x 9 L y 9 L z )Greek symbols e Energy parameter in the LJ potential rLength parameter in the LJ potential t w Fluid velocity at the channel wall t w h i Average fluid velocity at the channel wall 1 Introduction

Particle Based Simulation of Fluid Flow in Periodically Grooved Channels

“…We observe that as the conservative force increases the number density inside the cavities and near the walls become higher and more distant from the wall, a behavior which is called layering (for a more detailed description see Kasiteropoulou et al [31]). This behavior is in qualitative agreement with the results of Sofos et al [36] who investigated the surface wettability effects on flow in rough nanochannels and found that as the wall hydrophobicity decreases there is a kind of increased fluid atom localization. Actually we observe that the wall surface behaves more like a hydrophobic one as the conservative force parameter increases.…”

“…4a. We observe that in the main core of the channel the flow velocity increases significantly as the fluid/wall interaction also increases and this behavior is also presented in the work of Sofos et al [36]. This behavior can be explained by the equations (1) and (8).…”

Molecular dynamics simulation on flows in nano-ribbed and nano-grooved channels

“…This ratio was also found to be analogous to surface wettability (hydrophobic or hydrophilic wall), as potential energy values reveal wall/ fluid attraction for values ε w ε f = 1.5 (hydrophilic) and fluid atom repel from the wall when ε w ε f = 0.5 (hydrophobic) in [43].…”

“…This is attributed to the fact that grooves introduce an asymmetry to the flow, which is more pronounced for the hydrophilic cases, as the effect of the walls on fluid atoms extends over a greater range (see potential maps in [43]). Wall ribs do not seem to induce any kind of asymmetry.…”

Using mathematical models to understand the effect of nanoscale roughness on protein adsorption for improving medical devices

“…9 Cumulatively, there is plenty of evidence showing enhanced cellular functions on nanophase materials compared with their nanosmooth counterparts. 7 Specifically in orthopedics, some of the chemistries that demonstrate higher cellular adhesion and long-term cellular functions upon the creation of a nanophase topography are TiO 2 , Al 2 O 3 , hydroxyapatite, poly(lactic-co-glycolic acid) (PLGA), carbon nanotubes, and carbon nanofibers. 10,11 Although the list can be expanded with various other surface chemistries and tissue types, the major reason for this enhancement in cellular functions has been correlated with the interaction of the adherent cells with the initially adsorbed proteins on to the biomaterial surface.…”